Fast-gas switching for etching

ABSTRACT

A method for etching a layer in a plasma chamber with an inner injection zone gas feed and an outer injection zone gas feed is provided. The layer is placed in the plasma chamber. A pulsed etch gas is provided from the inner injection zone gas feed at a first frequency, wherein flow of pulsed etch gas from the inner injection zone gas feed is ramped down to zero. The pulsed etch gas is provided from the outer injection zone gas feed at the first frequency and simultaneous with and out of phase with the pulsed etch gas from the inner injection zone gas feed. The etch gas is formed into a plasma to etch the layer, simultaneous with the providing the pulsed etch gas from the inner injection zone gas feed and providing the pulsed gas from the outer interjection zone gas feed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to pendingU.S. application Ser. No. 13/958,239 filed on Aug. 2, 2013 and entitled“Continuous Plasma Etch Process,” which is incorporated herein byreference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.More specifically, the invention relates to the formation ofsemiconductor devices require etching features.

During semiconductor wafer processing during an etch different plasmaprocesses may be used.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method of for etching a layer in a plasma chamberwith an inner injection zone gas feed and an outer injection zone gasfeed is provided. The layer is placed in the plasma chamber. A pulsedetch gas is provided from the inner injection zone gas feed at a firstfrequency, wherein flow of pulsed etch gas from the inner injection zonegas feed is ramped down to zero during providing the pulsed etch gasfrom the inner injection zone gas feed. The pulsed etch gas is providedfrom the outer injection zone gas feed at the first frequency andsimultaneous with and out of phase with the pulsed etch gas from theinner injection zone gas feed, wherein the outer injection zonesurrounds the inner injection zone, wherein flow of pulsed etch gas fromthe outer injection zone gas feed is ramped down to zero duringproviding the pulsed etch gas from the outer injection zone gas feed atthe first frequency. The etch gas is formed into a plasma to etch thelayer, simultaneous with the providing the pulsed etch gas from theinner injection zone gas feed and providing the pulsed gas from theouter interjection zone gas feed.

In another manifestation of the invention, a method of for etching alayer in a plasma chamber with an inner injection zone gas feed and anouter injection zone gas feed is provided. The layer is placed in theplasma chamber. A pulsed etch gas is provided from the inner injectionzone gas feed at a first frequency. The pulsed etch gas is provided fromthe outer injection zone gas feed at the first frequency andsimultaneous and out of phase with the pulsed etch gas from the innerinjection zone gas feed. The etch gas is formed into a plasma to etchthe layer, simultaneous with the providing the pulsed etch gas from theinner injection zone gas feed and providing the pulsed gas from theouter interjection zone gas feed.

In another manifestation of the invention, an apparatus for etching anetch layer on a wafer is provided. A plasma processing chamber,comprising chamber wall forming a plasma processing chamber enclosure. Asubstrate support supports a wafer within the plasma processing chamberenclosure. A pressure regulator regulates the pressure in the plasmaprocessing chamber enclosure. At least one electrode provides power tothe plasma processing chamber enclosure for sustaining a plasma. Aninner injection zone gas feed provides gas into the plasma processingchamber enclosure. An outer injection zone gas feed surrounding theinner injection zone gas feed provides gas into the plasma processingenclosure. A gas outlet for exhausts gas from the plasma processingchamber enclosure. At least one RF power source is electricallyconnected to the at least one electrode. A gas source is provided. Aswitch with a switching speed of at least 1 Hz is in fluid connectionbetween the gas source and the inner injection zone gas feed and theouter injection zone gas feed, wherein the switch is able to provide apulsed gas to the inner injection zone gas feed at a first frequency andis able to provide the pulsed gas to the outer injection zone gas feedat the first frequency and out of phase with providing the pulsed gas tothe inner injection zone gas feed.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIGS. 2A-B are schematic cross-sectional views of a stack processedaccording to an embodiment of the invention.

FIG. 3 is a schematic view of a plasma processing chamber that may beused in practicing the invention.

FIG. 4 illustrates a computer system, which is suitable for implementinga controller used in embodiments of the present invention.

FIGS. 5A-B are graphs of the etch gas pulses.

FIG. 6 is a graph of a wafer by-product distribution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate understanding, FIG. 1 is a high level flow chart of aprocess that may be used in an embodiment of the invention which etchesfeatures. A substrate is provided with an etch layer (step 104). An etchgas is pulsed from an inner injection zone gas feed at a first frequency(step 108). An etch gas is pulsed from an outer injection zone gas feedat the first frequency and out of phase with the pulsed etch gas fromthe inner injection zone gas feed (step 112). The etch gas is formedinto a plasma (step 116).

EXAMPLE

In an example of an implementation of the invention, a substrate isprovided with an etch layer under a mask with features into a plasmaprocessing device (step 104). FIG. 2A is a cross sectional view of astack 200 with a substrate 204 disposed below an etch layer 208,disposed below a patterned mask 212 with features 216. In this example,the etch layer 208 is silicon. The etch layer 208 may be a siliconlayer, such as polysilicon, deposited on the substrate 204, or may bepart of the substrate 204. The patterned mask 212 is formed from siliconoxide. In various embodiments, one or more layers may be placed betweenthe various layers. For example, one or more layers, such as an etchstop layer, may be between the etch layer 208 and the substrate 204.

FIG. 3 schematically illustrates an example of a plasma processingsystem 300 which may be used to perform the process of etching the etchlayer 208 in accordance with one embodiment of the present invention.The plasma processing system 300 includes a plasma reactor 302 having aplasma processing chamber 304 therein. A plasma power supply 306, tunedby a match network 308, supplies power to a TCP coil 310 located near apower window 312 to create a plasma 314 in the plasma processing chamber304 by providing an inductively coupled power. The TCP coil (upper powersource) 310 may be configured to produce a uniform diffusion profilewithin the plasma processing chamber 304. For example, the TCP coil 310may be configured to generate a toroidal power distribution in theplasma 314. The power window 312 is provided to separate the TCP coil310 from the plasma processing chamber 304 while allowing energy to passfrom the TCP coil 310 to the plasma processing chamber 304. A wafer biasvoltage power supply 316 tuned by a match network 318 provides power toan electrode 320 to set the bias voltage on the substrate 204 which issupported by the electrode 320. A controller 324 sets points for theplasma power supply 306 and the wafer bias voltage power supply 316.

The plasma power supply 306 and the wafer bias voltage power supply 316may be configured to operate at specific radio frequencies such as, forexample, 13.56 MHz, 27 MHz, 2 MHz, 400 kHz, or combinations thereof.Plasma power supply 306 and wafer bias voltage power supply 316 may beappropriately sized to supply a range of powers in order to achievedesired process performance. For example, in one embodiment of thepresent invention, the plasma power supply 306 may supply the power in arange of 50 to 5000 Watts, and the wafer bias voltage power supply 316may supply a bias voltage of in a range of 20 to 2000 V. In addition,the TCP coil 310 and/or the electrode 320 may be comprised of two ormore sub-coils or sub-electrodes, which may be powered by a single powersupply or powered by multiple power supplies.

As shown in FIG. 3, the plasma processing system 300 further includes agas source/gas supply mechanism 330. The gas source/gas supply mechanism330 provides gas to a switch 332, which supplies gas to a gas feed 336in the form of a nozzle. The gas feed 336 has an inner passage 346 andouter passages 348. In this embodiment, eight outer passages 348surround the inner passage 346. In this embodiment, the switch 332 is afast switch which is able to provide pulses of gas to the inner andouter passages 346, 348 at a frequency of at least 1 Hz. In thisembodiment the switch 332 comprises an inner switch 333, which suppliesa gas to the inner passage 346, and an outer switch 335, which suppliesa gas to the outer passages 348. In another embodiment, sub-switches arenot used to control the pulsing of gas to the inner passage 346 and theouter passages 348, so that the switch 332 switches the flow of the gasfrom the inner passage 346 to the outer passage 348 and back. In thisembodiment, a periphery gas source 334 provides gas to periphery gasinlets 338. The process gases and byproducts are removed from the plasmaprocessing chamber 304 via a pressure control valve 342 and a pump 344,which also serve to maintain a particular pressure within the plasmaprocessing chamber 304. The gas source/gas supply mechanism 330 andperiphery gas source 334 are controlled by the controller 324. Amodified Kiyo by Lam Research Corp. of Fremont, Calif., may be used topractice an embodiment of the invention.

FIG. 4 is a high level block diagram showing a computer system 400,which is suitable for implementing a controller 324 used in embodimentsof the present invention. The computer system may have many physicalforms ranging from an integrated circuit, a printed circuit board, and asmall handheld device up to a huge super computer. The computer system400 includes one or more processors 402, and further can include anelectronic display device 404 (for displaying graphics, text, and otherdata), a main memory 406 (e.g., random access memory (RAM)), storagedevice 408 (e.g., hard disk drive), removable storage device 410 (e.g.,optical disk drive), user interface devices 412 (e.g., keyboards, touchscreens, keypads, mice or other pointing devices, etc.), and acommunication interface 414 (e.g., wireless network interface). Thecommunication interface 414 allows software and data to be transferredbetween the computer system 400 and external devices via a link. Thesystem may also include a communications infrastructure 416 (e.g., acommunications bus, cross-over bar, or network) to which theaforementioned devices/modules are connected.

Information transferred via communications interface 414 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 414, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, aradio frequency link, and/or other communication channels. With such acommunications interface, it is contemplated that the one or moreprocessors 402 might receive information from a network, or might outputinformation to the network in the course of performing theabove-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon the processors or may executeover a network such as the Internet in conjunction with remoteprocessors that shares a portion of the processing.

The term “non-transient computer readable medium” is used generally torefer to media such as main memory, secondary memory, removable storage,and storage devices, such as hard disks, flash memory, disk drivememory, CD-ROM and other forms of persistent memory and shall not beconstrued to cover transitory subject matter, such as carrier waves orsignals. Examples of computer code include machine code, such asproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Computer readable media mayalso be computer code transmitted by a computer data signal embodied ina carrier wave and representing a sequence of instructions that areexecutable by a processor.

Etch gas is pulsed from the inner injection zone gas feed at a firstfrequency (step 108). In this example the etch gas is 200 sccm Cl₂(Chlorine). A chamber pressure is set at 20 mT. In other embodiments,the pressure chamber may range from sub-milliTorr to 1 Torr (0.1 mT to 1Torr). In other embodiments, the etch gas comprises a halogen containingcomponent or a fluorocarbon containing component. In this embodiment,the inner injection zone gas feed is the outlet of the inner passage346. FIG. 5A is a graph of pulsing of the inner injection zone gas feed.In this example, the pulse 504 for the inner injection zone gas feedbegins at 1 second and lasts for 3 seconds before the flow is reduced to0%. The flow again begins at 8 seconds and lasts for 3 seconds.Therefore, the pulse 504 for the inner injection zone gas feed has aperiod of 7 seconds with a frequency of 1/7 Hz and a duty cycle of 3/7or about 43%.

The etch gas is pulsed from the outer injection zone gas feed (step112). Preferably the etch gas is pulsed from the outer injection zonegas feed at the first frequency and out of phase with the pulsed etchgas from the inner injection zone gas feed. In this embodiment, theouter injection zone gas feed is the outlet of the outer passages 348.FIG. 5B is a graph of pulsing of the outer injection zone gas feed. Inthis example, the pulse 508 for the inner injection zone gas feed beginsat 3 seconds at 50% and lasts for 4 seconds before the flow is reducedto 0%. The flow again begins at 10 seconds and lasts for 4 seconds.Therefore, the pulse 508 for the inner injection zone gas feed has aperiod of 7 seconds with a frequency of 1/7 Hz and a duty cycle of 4/7or about 57%. In this example, the pulse 504 for the inner injectionzone gas feed and the pulse 508 for the outer injection zone gas feedoverlap for 1 second. In addition, there is a 1 second period betweenthe end of the pulse 508 for the outer injection zone gas feed and thebeginning of the pulse 504 for the inner injection zone gas feed. FIGS.5A-B show that the pulsed etch gas from the outer injection zone gasfeed at the first frequency pulsed simultaneously with and out of phasewith the pulsed etch gas from the inner injection zone gas feed.

The etch gas is formed into a plasma (step 116). In this example, TCPpower is provided in a range of 1 W-4000 W. A bias voltage is providedin a range from 0 V-3000 V. The forming the etch gas into a plasma issimultaneous with the providing the pulsed etch gas from the innerinjection zone gas feed and providing the pulsed gas from the outerinterjection zone gas feed. FIG. 2B is a cross-sectional view of thestack 200 after features 216 are completely etched.

This embodiment provides a steady and constant etch gas that is pulsedout of phase between the inner injection zone gas feed and the outerinjection zone gas feed. Allowing for independent duty cycles, whilemaintaining the same frequency with a different phase allows additionaltuning knobs to provide a more uniform etch across the surface of thesubstrate. Preferably, the pulsing causes the flow to the innerinjection zone gas feed and the outer injection zone gas feed to rampdown to zero.

FIG. 6 is a graph of a wafer by-product distribution in a Kiyo chambergraphing steady state SiCl₄ mass fraction versus distance in cm from thecenter of the substrate. Curve 604 is the resulting wafer by-productdistribution, if the etch gas was supplied only to the inner injectionzone only through the inner passage 346. The SiCl₄ mass fraction isalmost 1.0 near the center, dropping to about 0.6 at 15.0 cm from thecenter. This results in about a 40% difference in the SiCl₄ massfraction between the center and edge of the substrate. Curve 608 is theresulting wafer by-product distribution, if the etch gas was suppliedonly to the outer injection zone only through the outer passages 348.The SiCl₄ mass fraction is about 0.3 near the center, rising to about0.8 at 15.0 cm from the center. This results in more than a 100%difference in the SiCl₄ mass fraction between the center and edge of thesubstrate. Curve 612 is the average of curve 604 and 608, which would beprovided by alternating pulses to the inner injection zone and the outerinjection zone with equal duty cycles. The SiCl₄ mass fraction is about0.6 near the center, rising to about 0.7 at 15.0 cm from the center.This results in about a 17% difference in the SiCl₄ mass fractionbetween the center and edge of the substrate. This lower percentdifferent in the SiCl₄ mass fraction between the center and edge of thesubstrate indicates a more uniform etch across the entire surface of thewafer. In a gas-pulsed process, by-products can be pumped out in betweengas flow events before initiating the next reaction sequence. Incontrast, in a continuous gas flow method even with both zonesoperational, the reactants and by-products are always in interactionduring the entire process, which may be detrimental.

In this embodiment, the inner injection zone gas feed is above a centerof the layer and directs the etch gas directly towards the center of thelayer, and the outer injection zone gas feed directs the etch gas at anacute angle with respect to the layer, as shown in FIG. 3. In addition,in this embodiment, the outer injection zone gas feed directs the etchgas away from the center of the layer.

In other embodiments of the invention, the periphery gas inlets 338 maybe used as the outer injection zone gas feed and the inner passage 346and/or outer passages 348 form the inner injection zone gas feed. Inanother embodiment, both the periphery gas inlets 338 and the outerpassages 348 form the outer injection zone gas feed and the innerpassage 346 forms the inner injection zone gas feed. In theseembodiments, the outer injection zone surrounds the inner injectionzone.

In another embodiment, the inner passage 346 forms the inner injectionzone gas feed, the outer passages 348 form the outer injection zone gasfeed, and the periphery gas inlets 338 provide a tuning gas. The tuninggas may be pulsed. In one embodiment, the frequency of the pulse of thetuning gas is different than the frequency of the pulse of the etchinggas. In another embodiment, the frequency of the pulse of the tuning gasis equal to the frequency of the pulse of the etching gas. In anotherembodiment, the periphery gas inlets 338 are not used or are notpresent.

Although the preferred embodiment uses an inductive coupling forenergizing the plasma, other embodiments may use other methods, such ascapacitive coupling to energize the plasma. In other embodiments, thenozzle may be replaced by a shower head. In other embodiments, thepulses are not square wave pulses.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

What is claimed is:
 1. A method for etching a layer over a substratesupported on a substrate support in a plasma chamber with an innerinjection zone gas feed and an outer injection zone gas feed, whereinthe inner injection zone gas feed is above the substrate support andwherein the outer injection zone gas feed surrounds the inner injectionzone gas feed and wherein at least part of the outer injection zone gasfeed is outside an outer edge of the substrate support, comprising:providing a pulsed etch gas from the inner injection zone gas feed at afirst frequency, wherein flow of pulsed etch gas from the innerinjection zone gas feed ramps down to zero during providing the pulsedetch gas from the inner injection zone gas feed, and wherein the pulsedetch gas from the inner injection zone is directed to the layer onsubstrate supported by the substrate support; providing the pulsed etchgas from the outer injection zone gas feed at the first frequency andsimultaneous with and out of phase with the pulsed etch gas from theinner injection zone gas feed, wherein the outer injection zonesurrounds the inner injection zone, wherein flow of pulsed etch gas fromthe outer injection zone gas feed ramps down to zero during providingthe pulsed etch gas from the outer injection zone gas feed at the firstfrequency; and forming the etch gas into a plasma to etch the layer,simultaneous with the providing the pulsed etch gas from the innerinjection zone gas feed and providing the pulsed etch gas from the outerinterjection zone gas feed.
 2. A method for etching a layer over asubstrate supported on a substrate support in a plasma chamber with aninner injection zone gas feed and an outer injection zone gas feed,comprising: providing a pulsed etch gas from the inner injection zonegas feed at a first frequency; providing the pulsed peripheral gas fromthe outer injection zone gas feed at the first frequency andsimultaneous and out of phase with the pulsed etch gas from the innerinjection zone gas feed; and forming the etch gas into a plasma to etchthe layer, simultaneous with the providing the pulsed etch gas from theinner injection zone gas feed and providing the pulsed peripheral gasfrom the outer interjection zone gas feed, wherein the inner injectionzone gas feed is above the substrate support and wherein the outerinjection zone gas feed surrounds the inner injection zone gas feed andwherein at least part of the outer injection zone gas feed is outsidethe outer edge of the substrate support.
 3. The method, as recited inclaim 2, wherein flow of pulsed etch gas from the inner injection zonegas feed ramps down to zero during pulsing.
 4. The method, as recited inclaim 3, wherein flow of pulsed peripheral gas from the outer injectionzone gas feed ramps down to zero during pulsing.
 5. The method, asrecited in claim 2, wherein the outer injection zone gas feed isvertically located below the inner injection zone gas feed.
 6. Themethod, as recited in claim 2, wherein the pulsed peripheral gascomprises at least one of an etch gas, a tuning gas, an inert gas, or adeposition gas.
 7. The method, as recited in claim 2, wherein the pulsedperipheral gas is the etch gas provided by the inner injection zone gasfeed.
 8. The method, as recited in claim 2, wherein the inner injectionzone gas feed directs the etch gas directly towards a center of thelayer.
 9. The method, as recited in claim 2, wherein part of the outerinjection zone is above and within the outer edge of the substratesupport.
 10. The method, as recited in claim 2, wherein the pulsed etchgas has a frequency of at least 1 Hz.